1. Field of the Invention
This invention relates generally to water heating apparatus, and more particularly to vent dampers and flue closures for gas hot water heaters.
2. Brief Description of the Prior Art
In gas water heaters, fuel is burned in a combustion chamber located at the base of the heating unit. The water contained in the heater tank is heated by conduction through the combustion chamber where the fuel is burned, as well as by conduction through the heater's central venting passageway through which the hot combustion gases pass. These combustion gases are then exhausted via a flue.
Even after the flame is extinguished in the combustion chamber, the heated water maintains sufficient heat in the walls forming the central passageway to induce a flow of cooler ambient air therethrough. The passage of the cooler air causes substantial energy loss as the heated water is caused to cool more rapidly than would be the case if the cool ambient air were not allowed to pass through the tank and into the flue.
Existing types of flue dampening devices usually comprise a hinged, one-way mechanical valve that prevents outside air from passing through the exhaust flue. However, these devices require a significant flow of exhaust in order to open, and thus are used mostly with units having a fan or blower. Other damping devices utilize a bi-metal expansion/contraction valve to regulate flow.
Applicant's prior U.S. Pat. No. 4,770,160 discloses a more efficient form of vent damper which is incorporated into the central exhaust passageway above a hot water heater. The damper comprises a frusto-conical shaped floating poppet closure that is slidably mounted on a guide within a flue hood immediately above the heater. When the heater burner is in operation, the hot exhaust gases lift the poppet allowing the gases to escape around the poppet and into the flue. When the main burner is off, the poppet lowers into a closed position where it rests atop the tank's central passageway. In this is position, the poppet blocks the passageway and prevents the cool room air from circulating therethrough. This closure saves energy by slowing the cooling of the water and thus conserving the heat within the water tank.
Although the frusto-conical or dome shaped poppet closure provides a substantial improvement over the prior art, the shape of the poppet interrupts the vertical flow of the exhaust gas, and directs it almost horizontally. Re-directing the exhaust flow increases the risk of spillage of the exhaust gas into the building space housing the water heater. In addition, the shape of the poppet makes it expensive to manufacture, and its engagement to its guide sometimes affects its reliability.